The invention is directed to an assembly for sealing the space around instrument leads passing through the cover of a pressure vessel containing fluids which are to be prevented from leaking out of the vessel.
Specifically, the invention relates to a device for use in the Experimental Breeder Reactor No. II (EBR-II) whereby expensive and delicate stainless-steel-clad instrument leads, which must be conducted through a cover of a primary tank surrounding the reactor core, may be adequately sealed against leakage of gas and vapor and at the same time be protected so that reuse of the same leads is possible without damaging them upon removal from the seal. EBR-II is described in Solid Fuel Reactors, Ch. 3, pp. 118 to 238 (J. R. Dietrich and W. H. Zinn ed. 1958; Addison-Wesley Publishing Company, Inc., Reading, Mass.)
In nuclear reactors designed for test and experimental purposes, it is frequently necessary to measure variables in the reactor core during reactor operation. Due to intense radiation and high temperature, such measurements are taken within the core but indicated remotely outside of the primary tank which contains a pool of liquid sodium in which the core is submerged. For this purpose, test assemblies are inserted into the core through the primary tank cover so that parameters such as coolant flow, temperature, pressure, etc., may be measured at many different known locations. The test assemblies contain stainless-steel-clad leads which connect to instruments, experiment capsules, or detectors at various positions along the test assembly. The group of leads associated with each test assembly must be brought out to external instrumentation through the primary tank cover. The bodies to which the ends of any given lead are connected may be many times larger in diameter than the lead itself. However, at the same time leakage to atmosphere of argon gas and sodium vapor above the sodium pool in the primary tank must be prevented because of the radioactivity and explosion hazards to persons outside the primary tank. In the past, this has required that the leads be welded or brazed into a larger seal body which then may be installed in the primary tank cover and sealed by conventional gasket means. However, removal of the instrumentation from the test assembly results in destruction of the instrument leads. A purpose of the invention is to enable the leads to be removed from the seal and the reactor with no damage to the leads or seal so that both the seal assembly and the leads may be reused as many times as desired. Also, if the lead is sealed to two larger bodies, the invention provides a way of sealing without using a large clamping seal through which one of the larger bodies would have to pass. Hence, the sealing is accomplished in a small area and conserves valuable space in the crowded access area above the primary tank cover.